The present invention relates to diver-operated tools, and more particularly, to diver-operated tools using water jets to erode submerged articles. Such tools are used for a variety of applications, including removing marine growths from surfaces so as to permit either inspection or repairs; stripping off concrete "weight-coats" from underwater steel pipelines which contain gas or oil to allow for repair or modification of these pipelines; and stripping off coal-tar based protective paint coatings from steel members, again to permit repair of modification. Conventional water jet diver-operated tools typically provide some means for countering the thrust force exerted by the erosive jet on the front end of the tools. Without this counterthrust means, the diver would be continually forced backwards in the water by the thrust of the erosive jet, and would thus have to exert considerable wasted energy in order to maintain his desired working position.
Conventional diver-operated water jet tools merely divert fifty percent of the water flow available to the tool through a counterthrusting water jet nozzle affixed to the back end of the tool. This counterthrusting water jet-forming nozzle thus develops a force which is equal to magnitude but opposite in direction to the force created by the erosive water jet on the front end of the tool. In this manner, the tool attains a force balance, and hence can be more easily deployed by the diver.
In such conventional water jet tools, fully one-half of the available hydraulic power (from the high-pressure pump used to feed the water to the tool) is thus not being used for performing the work intended, namely cleaning or cutting a substance with the erosive jet.
The nozzles used to form the erosive jet in conventional diver tools are not designed to create cavitation in an effective fashion. Nozzles designed to create effective cavitation have proven to be capable of much more rapid and efficient cleaning and cutting when compared to conventional nozzles delivering the same flow rate with an equal pressure drop across the nozzles.
Because of the considerable expense involved in performing underwater work with a team of divers, it is very desirable to provide the divers with the most efficient and effective tools possible, within economic boundaries. Although one alternative for increasing the cleaning or cutting effectiveness of underwater erosive water jet tools is to purchase and operate pumps which produce larger flow rates of water at higher pressures, such higher capacity pumps are increasingly expensive to purchase and operate. However, higher flow rates require larger, more expensive, and unwieldy hoses to transfer the water from the pump to the diver-operated cool. Furthermore, despite careful balancing, there are limits to the amount of total power that a diver can safely handle. Although higher pressure (than the conventional 10,000 psi commonly used with diver tools) will increase cleaning the cutting rates, there are many drawbacks to this approach, which include: greater danger if the erosive jet is misdirected or if any hoses, fittings, or pipes are broken; shorter lifetimes for all system components, including nozzles, hoses, pump seals, and packings; and greater expense in the purchase, maintenance, and replacement of very high pressure components. Also, higher pressures require a higher horsepower for the diesel engine typically used to drive the pump, and hence a greater fuel cost for operation of the system.
It is therefore desirable to provide a water jet erosive tool for divers which can most efficiently utilize a minimized amount of hydraulic power, i.e., minimized flow rates for the water and minimized pump pressures. The present invention significantly improves the usage of available hydraulic power. It has been demonstrated in numerous comparative tests that the tool of the present invention is capable of substantially faster rates of cleaning and cutting when compared to conventional water jet diver tools.